In recent years, EL elements using organic materials and inorganic materials, such as rare earth-added ZnS and BaAl2S4, for the light-emitting layer have been developed. But, a problem of such EL elements is that the light emission characteristics are drastically degraded by atmospheric exposure. It is indicated that when EL elements are formed with these materials, wrapping technique and sealing technique during assembly are necessary, and their fabrication and manufacturing line are complicated. Therefore, the product cost is expensive. Furthermore, the raw materials used for the organic EL light-emitting layer are more expensive than platinum in terms of cost per gram and therefore are a factor of high cost. Further, in inorganic EL, the drive voltage is generally 200 V or more. Therefore, the drive power supply circuit is large, and slimming down is more difficult than in organic EL.
A perovskite oxide structure is simple and is of a chemically stable material. Therefore, elimination of degradation due to atmospheric exposure and elimination of aged degradation are expected. In recent years, the research and development of fluorescent materials with perovskite oxide polycrystal powders have been actively performed, and good fluorescence characteristics have been obtained. On the other hand, for epitaxial thin films, three primary colors of red, green, and blue, which are the basis of display fabrication, have also begun to be developed, and good fluorescence has been obtained, whereas EL provided by electric field application has not been obtained yet. In application to displays and the like, an EL element formed by sandwiching a light-emitting layer between dielectric layers on a thin film electrode material, with thin films, and fabricating an upper electrode is essential, and the development of a multilayer structure of dielectrics (used as the hole transport layer and the electron transport layer) and the light-emitting layer with thin films, and the development of an EL element achieving an interface control technique providing good adhesion between the dielectric and the electrode material are supposed to be urgently necessary.
For the fluorescence characteristics of oxide polycrystals, Non-Patent Document 1 shows that fluorescence characteristics are obtained by substitution with Ca, Sr, or Ba in a polycrystal ASnO3 perovskite structure. Non-Patent Document 2 shows that blue fluorescence is obtained in a polycrystal Sn, layered perovskite structure. Non-Patent Document 3 shows fluorescence characteristics when polycrystal CaSnO3 is substituted with Tb. Non-Patent Document 4 shows red fluorescence characteristics in a polycrystal, layered perovskite Srn+1TiO3n+1 system. Non-Patent Document 5 shows that regarding a SrTiO3 single crystal and thin film, blue white fluorescence occurs due to oxygen loss. Non-Patent Document 6 shows that red fluorescence characteristics are obtained when polycrystal SrTiO3 is substituted with a Pr atom. Non-Patent Document 7 shows the red fluorescence characteristics of polycrystal, Pr atom-substituted (CaSrBa) TiO3.
For the fluorescence characteristics of oxide thin films, Non-Patent Document 8 shows the blue fluorescence characteristics of a thin film, MHfO3:substituted-Tm. Non-Patent Document 9 shows the fluorescence characteristics of a BaTiO3 thin film substituted with an Er atom. Non-Patent Document 10 shows the red fluorescence characteristics of a thin film, CaSrTiO3:substituted-Pr. Patent Document 1 shows a method for manufacturing a double oxide phosphor thin film in which an inorganic base material, such as yttrium aluminate, is substituted with a metal ion. Patent Document 2 shows a method for manufacturing a thin film that emits light by the application of a mechanical external force, with a material containing a rare earth metal ion or a transition metal ion in an inorganic base material.
For the EL characteristics of oxide thin films, Non-Patent Document 11 shows the red light emission characteristics of a thin film EL element in which Ga2O3 is substituted with Eu. Patent Document 3 shows an inorganic-thin film EL element using a ceramic sheet as a transport layer.
For oxide polycrystals, Patent Document 4 shows the fluorescence characteristics of a polycrystal Sn perovskite oxide system. Patent Document 5 shows that the fluorescence characteristics of red, green, and blue, which are three primary colors of light, are obtained by a Ti thin film or a Sn thin film having an oxide perovskite structure. Patent Document 6 shows regarding an EL element using a Zn2SiO4:Mn thin film, which is a non-perovskite structure, for a light-emitting layer, a method for improving luminance and life.